This project proposes a study of the complement system and the interaction of genetic and acquired abnormalities of complement in the expression of rheumatic disease, particularly systemic lupus erythematosus, juvenile rheumatoid arthritis, and rheumatoid arthritis. New methods will be developed for the assay of immune complexes and the ability of cells to bind them. It is suggested that such investigations will better define mechanisms of tissue injury and the host factors that predispose to such insults; parameters might also be evolved which act as indices of disease activity for diagnostic and therapeutic purposes. BIBLIOGRAPHIC REFERENCES: Schur, P.H., Connelly, A. and Jones, T.C.: Phylogeny of complement components in non-human primates. J. Immunol. 114:270-273, 1975. Tannenbaum, H., Pinkus, G.S., Anderson, L.G. and Schur, P.H.: Immunologic characterization of the mononuclear cell infiltrates in rheumatoid synovia, in rheumatoid nodules, and in lip biopsies from patients with Sjogren's syndrome. Arthritis Rheum. 18:305-314, 1975.